In recent years, metal roller chains have come into increasing used in power transmissions, in automobile engines and in other machines, as a result of high loads, high speeds, and the demand for maintenance-free operation. Roller chain transmissions have displaced toothed belt transmissions to a large extent.
A typical roller chain transmission device comprises a roller chain including inner and outer links. Each inner link comprises a pair of inner link plates, two bushings, ends of which are press-fit into bushing holes formed in the inner link plates, and a roller rotatable on the outside of each bushing. Each of the outer links comprises a pair of outer link plates and two pins press fit into the outer link plates. The outer link plates of each outer link are in overlapping relationship with the inner link plates of two adjacent inner links, and a pin of each outer link extends loosely through a bushing of an adjacent inner link, whereby the inner and outer links are connected articulably in alternating relationship along the length of the chain. In the power transmission, the roller chain is typically in mesh with a drive sprocket and one or more driven sprockets.
Roller chains used in such a roller chain transmission device, include “A series” roller chains, which satisfy the relationships 0.59≦D/P≦0.64, and 0.28≦d/P≦0.38, and “B series” roller chains, which satisfy the relationships 0.57≦D/P≦0.67, and 0.28≦d/P≦0.38, D being the outer diameter of the roller, d being the outer diameter of the pin, and P being the chain pitch. These chains are chosen based on demands for a size balance and standardization (See Japanese Industrial Standard JIS B 1801).
Sprockets, having tooth forms which smoothly move at engagement with and disengagement from a roller chain and efficiently transmit rotational torque to a rotating shaft, are standardized, and a sprocket may be selected in accordance with the particular roller chain with which it is to be used.
To reduce noises generated at engagement between a chain and a sprocket, various approaches have been proposed. One is a low noise roller chain transmission device in which a roller and a chain are engaged with each other at a random pressure angle, by use of a roller chain in which two or more kinds of rollers having different outer diameters are randomly disposed along the length of the chain. Another uses a sprocket in which teeth having different shapes of flank surfaces are randomly disposed on the periphery of the sprocket. These approaches are described in Japanese laid-open Utility Model Publication No. Hei. 5-59014 and Japanese laid-open Patent Publication No. 2002-266988.
However, it has not been shown that the above-mentioned conventional low noise roller chain transmissions reduce engagement noise to any significant degree. Thus, to obtain an optimum reduction effect, it was necessary to use trial and error repeatedly.
Furthermore, it has been shown that a particularly large engagement noise between the roller and the chain occurs in specific regions of rotational speeds. However, in previous approaches to noise reduction, these abnormal noises, which occur at specific ranges of rotational speeds were not avoided.
Accordingly, taking the problems of the above-mentioned conventional roller chain transmission device into consideration, an object of the invention is to provide a roller chain transmission which reproducibly reduces engagement noises between a roller chain and a sprocket without the need for design by trial and error. Further, another object of the invention is to provide a roller chain transmission device, which suppresses abnormal noises which occur in specific regions of rotational speeds.